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When Serena Williams talks about her two daughters, you can just about hear her smile.

The 23-time Grand Slam champ recently shared her perspective on diet, exercise — and what it means to be the youngest sibling — in a phone interview with PEOPLE in conjunction with her new partnership with Lingo, a continuous glucose monitor from Abbott.

“Olympia was a solo child,” Williams, 43, says about Olympia, who was nearly 6 when Adira was born in August 2023. “She was our star. And I am so obsessed with Olympia. Even when I was pregnant, I was like, ‘How do I even love anyone as much as Olympia? It just doesn’t work.’ ”

But she adds, “It’s so funny how, I don’t know, just your heart gets bigger. I was just like, my heart just got bigger.”

Now, as the GOAT transitions from playing tennis to making school runs, she shares that her family dynamic growing up as the youngest of five sisters gives her a unique perspective in how she navigates the relationship between her 7-year-old and 15 month-old girls, whom she shares with husband Alexis Ohanian.

“Olympia is a very hard act to follow, but I tell you what, Adira has followed it and it’s just so crazy,” Williams tells PEOPLE. “She’s amazing. I just can’t wait for people to see how amazing she is in her own way. And she’s so special and she’s so tough. She’s just a tough little cookie. And she reminds me a lot of me in that aspect.”

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Recently, Adira showed an adorable side to her personality in a post on Instagram where she shared the tennis court — but not so much the balls — with one of the all-time greats.

Serena Williams and Alexis Olympia during the Auckland Classic tennis tournament in 2020.MICHAEL BRADLEY/AFP/Getty

“I have a little soft spot for the younger sister, so I’m like, ‘You go girl, you can do it too.’ ” Williams says. “And I love that.”

And as her younger daughter navigates toddlerhood, Williams is making sure to look out for little sis.

“I’m like Olympia, ‘Make sure you share your toys,’ ” Williams says. “I know what it’s like, I have to stick up for Adira.”

In her new partnership with Lingo, the tennis icon is also keeping a continuing eye on her health.

“I have to be with the kids, I have to drop ’em off at school. I have to do all these things,” she says. “So I’ve become really obsessed with what I put in my body, which is why I’ve been really pretty excited about Lingo and making the right choices for my health and wellness.”

At this point in the game, Williams is enjoying all of the advantages in her life after tennis.

“With my business with Serena Ventures, we invest in a ton of women and I just love introducing them to great big companies,” she says. “Honestly, it’s so exciting. It’s so exciting to be on those calls and to hear these women who would’ve never had this other opportunity otherwise. So my gift is going somewhere else now with investing, and being a mom, and it’s great.”